Sharif Digital Repository

Nanostructured graphene based membranes demonstrated excellent capabilities in various applications in nanofiltration and energy conversion due to unique atomically smooth surfaces and adjustable pore size or interlayers spacing at Angstrom scales.In addition to graphitic surface and physical confinement on ions in Graphene-oxide (GO) laminates, surface charges on such 2D-slits provide an attractive aspects to have more channels walls interactions with ions. There are some reports on the osmotic power generation using physical confinements and electrostatic interactions between ions and GO membranes. However, the results indicated insufficient power densities (1 W=m2 ) can be achieved... 

A 2D simulation has been carried out to study the effect of magnetic field on heat transfer and pressure drop of nanofluid flowing through a pipe filled with porous medium. The nanofluid flow is modeled as a single-phase flow, and Darcy–Brinkman–Forchheimer equation is employed to model fluid flow in porous media. A constant uniform heat flux was imposed on the walls of the cylinder, and the values of Darcy number, Hartmann number, and volume fraction of the nanoparticles were selected as 0.1, 200, and 0.2, respectively. Effects of parameters such as Reynolds number, the material of the porous medium (conductivity and porosity), and material of nanofluids have been investigated in the... 

The present work illustrates the results of an experimental study of ferrofluid flow in a tube subjected to a constant heat flux on its wall and filled with permeable material under the effect of magnetic field. The aim of this project is investigating the enhancement of heat transfer and obtaining a uniform temperature distribution inside the pipe. In order to achieve this, a porous medium with a porosity of 0.39 and ferrofluid with volume fractions of 0.6, 1.0 and 1.5 are used simultaneously, in the presence of magnetic field. The experiments are held for four different Reynolds numbers of 147.1, 167.3, 184.3 and 205.1. Also, four various modes of the oscillatory magnetic field are applied... 

Resistive pulse sensing (RPS) has proved to be a viable method for detection and characterization of micro and nano particles. This method works based on ionic current variation inside nanopores. Modern fabrication methods have introduced different nanopore geometries for resistive pulse sensors therefore studing the effects of geometry on sensing performance of nanaopores is important. Numerical simulation has been used to study a wide variation of nanopore’s geometry configurations and study the physics behind this phenomena. Based on the results, numerical simulation could be used as a fast and easy tool for size determination for nanopore. To compare the sensing performance of different... 

In the present study, mixed-convective heat transfer of nanofluids in a vertical rectangular channel partially filled with open-cell metal foam has been investigated experimentally and numerically. Al2O3–H2O nanofluids with different concentrations were synthesized and their stability was inspected with UV-Vis spectroscopy. The outlet temperature and pressure drop were measured for different nanofluid flow rates (i.e., Reynolds number values). In the numerical section, a two-dimensional volume-averaged form of the governing equations was used. The velocity and temperature profiles were obtained using finite difference method. The Brinkman–Forchheimer extended Darcy model and the... 

Pulsating heat pipe (PHP) is a two-phase device for the means of transferring high heat fluxes and is used extensively for the electronic cooling. In this study the different flow regimes in PHP with different fluids have been investigated. In this research, 3 different fluids including: Pure fluids, Ferro-fluid and surfactant solution with %50 filling ratio have been used. For ferro-fluid, 5 different concentrations and 3 type of magnetic fields have been operated in 2 different heat pipes. Results show that ferrofluid is more stable in Pyrex made-heat pipe for long period of time and no magnet mode has the best thermal performance due to high conductivity of fluid. In copper made-heat pipe... 

In this article, the problem of mixed convection in vertical rectangular microchannels for both regular fluids and nanofluids have been solved, using the CFD technique in the entrance regions of momentum and heat transfer taking in account the influences of viscous heating, inertial force and sleep conditions. In case of nanofluid flow, both the Brownian and thermophoresis molecular transfer mechanisms were considered.The predicted results were validated using fully developed distributions of velocity and temperature. Furthermore, the influences of mixed convection parameter (Gr/Re) and Kn number values on distributions of velocity and temperature through the entrance and fully-developed... 

Today, the usage of hollow membrane contactors is considered by the researchers as a novel solution in the separation and purification industry, including the sweetening of gas. Improving the performance of these devices requires a more detailed study of the process factors and changes in its chemistry. Hence, providing a suitable mathematical model by examining the details of the flow pattern within the contactor is based on the computational fluid dynamics technique in the agenda. Also, improving the absorption of components such as carbon dioxide and hydrogen sulfide from the gas mixture using chemical absorbents such as monoethanolamine will be investigated. The change in the mass... 

The advances of technology of microelectrical devices and their computational capacity and so, their heat rates, make the thermal control of them more complex. Utilizing nanopfluids is one of proposing options. The current research investigates the effectiveness of using nanoparticles on the heat transfer rate of fluids in the natural convection. A two-component two-phase lattice Boltzmann method (LBM) has been implemented for this purpose. A wide range of Rayleigh number (Ra), namely 103 to 109, 0 to 0.05 volume fraction s of nanoparticles and nanoparticle diameters below 100 nm has been investigated in this research. The method is optimized for complex geometries. Two and three dimensional... 

Despite of passing many years from invention of Computational Fluid Dynamics (CFD), simulation of the fluid-solid interfaces and free surfaces are still completely challenging and progressive problems. In addition knowing and understanding nanotechnology huge applications,modeling of nano-fluids have been became a priority for researchers. Adding importance of Non-Newtonian fluids (especially polymeric solutions) to this two subjects, triangle topics of this research becomes vivid. In this research tried to consider and examine behavior of Newtonian,Generalized-Newtonian, Viscoelastic and nano-filled viscoelastic fluids in one and two phase mediums. we followed mesh free methods which are... 

This project reports an experimental work on the convection heat transfer of nanofluids, made of -AL2O3 nanoparticles and de-ionized water, flowing through a copper tube in the laminar flow regime. The results showed considerable enhancement of convective heat transfer using the nanofluids. The enhancement was particularly significant in the entrance region, and was much higher than that solely due to the enhancement on thermal conduction. It was also shown that the classical Seider and Tate equation failed to predict the heat transfer behavior of nanofluids. Possible reasons for the enhancement were discussed. Migration of nanoparticles and the resulting disturbance of the boundary layer... 

One of the critical challenges in droplet based micro- and nanofluidic devices is handling the droplet breakup such that a controllable droplet size is produced. The experimental and numerical investigations at the microscale indicate that the droplet size can be well controlled by T junction geometries. In the present study we use non-equilibrium molecular dynamics (NEMD) simulations to investigate this phenomenon at the nanoscale. In order to generalize the study the Lennard-Jones type potential between the fluids and the walls have been considered and the strength and the effective range of the potential are changed to consider a wide variety of materials. Our results reveal that the... 

In terms of thermodynamics and heat transfer, heat pipes such as closed two-phase thermosyphon are of great importance in saving energy. In this study, a computational fluid dynamics model for simulation of a thermosyphon heat pipe with two-phase flow including phase change heat transfer was developed. The study has mainly focused on the effects of volume concentrations of Nanoparticles and the operating temperature on the heat transfer performance of the thermosyphon. The analysis was performed to compare heat transfer performance between a solid copper tube and a thermosyphon heat pipe which contained deionized water and graphene oxide(GO)/water Nanofluid as its working fluids. Based on a... 

Enhanced oil recovery (EOR) techniques are gaining more attention worldwide as the proved oil is declining and the oil price is hiking. Although many giant oil reservoirs around the world were already screened for EOR processes, the main challenges such as low sweep efficiency, costly techniques, possible formation damages, transportation of huge amounts of EOR agents to the fields especially for offshore cases and the lack of analyzing tools in traditional experimental works, hinder the proposed EOR process.It has been shown that recently, nanoparticles are attractive agents to enhance the oil recovery at the laboratory scale.
In this study TiO2 nanoparticles were used to improve... 

In this paper, carbon structures such as multi wall carbon nano tubes, graphene and hybrid graphene-iron oxide, for utilisation in wet cooling towers in order to improve heat transfer are being discussed. All synthesized nanoparticles are prepared by chemical vapour deposition and wet chemical methods. Nature and structure of the created particles is also being examined by using X-Ray diffraction, transmission electron microscope and scanning electron microscope. The water used in this research is a kind of brine water, currently being used in industrial cooling towers at oil-rich regions of southern Iran. Performing the ICP test on the available water and by exact determination of its... 

In this study, thermal and rheological properties of nanofluids of water/carbon nanotubes, water/spherical silica nanoparticles and water/hybrid nanoparticles (hybrid of carbon nanotubes and spherical silica nanoparticles) have been investigated. To do so, carbon nanotubes have been synthesized by CCVD process and spherical silica nanoparticles and hybrid nanoparticles by wet chemical method. After synthesis of nanomaterials, nanofluids have been prepared by using SDBS as a dispersant with the concentration of 1.5 times of concentration of nanomaterials and then thermal conductivity, kinematic viscosity, dynamic viscosity and density of nanofluids have been investigated. As the results show,... 

In this research convective heat transfer coefficient enhancement of nanofluids prepared from high surface area graphene has been investigated in laminar flow in the developing region. The nanofluid has been prepared from nanoporous graphene with high surface area and with concentration of 0.025 to 0.1 %wt. Deionized water has been used as the base fluid and a type of Ter-Polymer has been utilized as the surfactant. The results indicate that thermal conductivity of nanofluid with concentration of 0.1 %wt remains quite constant, with only %3.8 enhancement, while convective heat transfer coefficient improves significantly, with 34% enhancement. The behavior of this enhancement related to the... 

Experiments were performed to explore the free convective hat transfer characteristics of water based nanofluids. Experiments of natural convection over a vertical flat plate with constant heat flux in water-based nanofluids with Ag and TiO2 nanoparticles were performed. Velocity boundary layer measured using PIV method. Also convective heat transfer coefficient obtained using three thermometers behind the wall. Various test cases with different heat fluxes on the wall are considered. Two volumetric concentrations of Ag nanofluid, 1% and 2%, and TiO2 nanofluid, 1% and 2%, were tested in the present study. It was shown that, with increasing nanofluid concentration, velocity boundary layer... 

In the present work, the experiments were carried out for two types of PAM (3330 and 3630) with three distinct concentrations (25, 40 and 55 ppm) and TiO_2-water nanofluid for four concentrations (1.5, 2, 2.5 and 3 vol. %), and the Nusselt number and friction factor for each of them expressed separately. The Reynolds number was in the range from 11000 to 21000. The steady state turbulent convective heat transfer and friction factor of the combination of TiO_2-water nanofluid and polymer 3330 in the coiled tube were investigated. The effects of the Reynolds number for 2 vol. % nanoparticles which consists of 25 ppm PAM (3330) determined at the constant temperature of 24°C. It was observed... 

Inhencemant of automobile radiator heat performance is the purpose of this study. Radiator fin shape, coolant fluid properties and influence of nanofluid studied in this research. Plain fin, louvered fin and vortex generator fin is choosen and design. With flow simulation influence of fin shape on heat performance is studied. After that, with considering radiator coolant fluid, the effect of antifreezing on fin heat transfer is evaluated. Then by addin nanoparticles to water and antifreezing solution, effect of nanofluid on heat transfer is evaluated. Results show that with increasing the air velocity for all geometries in the study , heat transfer and pressure drop is increased. But heat...